Cambridge University did not want to comment, saying that it was a matter for the police. Cambridgeshire Police has only said :"Officers use covert tactics to gather intelligence, in accordance with the law, to assist in the prevention and detection of criminal activity."

Today my colleague Hugh Muir takes an acerbic look at how "the secret snoopy state seeks to monitor the legitimate activity of those who might ask questions of it."

They added :"Tactics such as these are not only intrusive, they also waste time targeting groups which are involved in making important and positive change in our society. We condemn the actions of the police in this matter and hope the Government will look critically at the use of surveillance measures by UK security forces."

Cambridge Defend Education, an anti-cuts campaign named as a potential target of the infiltration, said :"The police will go to any lengths to gain 'intelligence' on activist groups, including deceiving women into long-term intimate relationships. It is telling that the police regard their activities as completely legitimate and legal, reflecting their crucial role in enforcing austerity policies through both violent and covert repression of those who oppose them."

Rachel Wenstone, deputy president of the National Union of Students, said : "This revelation is an absolute scandal. This is yet another example of the questionable tactics that undercover police officers have taken in recent years to infiltrate campaign groups and extract information.We now need to know just how widespread this practice is."

She added : "To group the activities of hardworking students' unions within the same realm as those of the English Defence League is grossly offensive."

The covertly-recorded footage had shown that the police officer also wanted information about the EDL, but recognised that the activist was on the wrong side of the political divide to provide those details.

Nick Pickles, director of Big Brother Watch, condemned the infiltration of "anti-fracking or educational campaign groups, where there is zero suspicion of any wrongdoing" as "a gross abuse of surveillance powers."

"Coming after attempts to discredit the family of Stephen Lawrence and undercover officers fathering children with activists this episode makes clear why the police should not be able to approve their own undercover surveillance operations. Judicial oversight is essential if these kinds of abuses are to be prevented.

"Were it not such a stark reminder of the weak oversight of police intelligence operations you'd be forgiven for thinking this was the plot for a student film, albeit inspired more by David Brent than James Bond."

"There should be a full, independent inquiry into the activities of this unit and I will be writing to the Independent Police Complaints Commission to ask that they investigate."

Jules Carey, a solicitor at Tuckers' law firm representing several campaigners taking action against the Metropolitan Police over the alleged behaviour of undercover officers, said of Cambridgeshire Police: "The force has clearly lost its way. There can be no justification in a democracy for attempting to deploy informants into student groups and protest organisations. The force should be seeking to uphold the fundamental right to protest, not taking cynical steps to undermine it".

"That any group which dares to dissent is apparently fair game should alarm anyone committed to proportionate policing and democracy itself. Proper judicial checks on police surveillance are badly overdue - Parliament must take responsibility and act."